I'm not sure what version of Blender is used in the tutorial but in Blender 4.0, when plugging the RGB node into the Roughness or Metallic input of the BSDF node, the color goes white.
Also, the BSDF node looks different with each of the major sections being collapsed. When expanding each, I find that the options are different. There is no Specular slider. Instead, there are is only "Weight, Radius, Scale & Anistropy" inputs. I do not know which of these inputs correspond to the Subsurface input shown in the video lesson. This also became a point of contention in a different class I took before.
The behavior of plugging a Color Output (yellow) into a Value Input (grey) hasn't changed. Blender takes the Luminance ('average human perceived brightness') of the Color and uses that. This is the same as using a Converter > RGB TO BW Node inbetween. Don't know why you get white... (maybe it's from the (environment) lighting...
A lot of the changes in the new Principled BSDF are 'internal"
The Specular slider has just been renamed.(Specular > IOR Level). The Sheen is completely new and much improved. Biggest user change is with the Subsurface Scattering. The Weight slider in Subsurface is like the Metallic Slider: typically either 0 or 1.
In a picture (not completely accurate, but gets you started):
You will find this type of issue a lot with Blender, it just changes too fast, there is no way to keep up with it. If you are using the latest version, in the beginning nothing will match with the content that is out there. That is why it is always recommended to use the Blender version the tutorial was recorded with. The overall knowledge is more important than the where did they put this button. So I 100% suggest you do a course with its respective version of Blender.
